Memory systems are used in nearly all microprocessor and digital equipment applications. Memory systems generally utilize different types of memory for different applications. Memory systems generally include a memory array that has a large number of memory cells arranged in an array of rows and columns. Each memory cell has a specific address that corresponds to its respective row and column. Retrieving data from an individual memory cell is generally accomplished by activating the respective row of memory cells and then reading only the respective column to obtain the data in the memory cell.
The power required to operate the memory system is a primary concern in most applications. For example, in limited power applications, such as a battery powered laptop computer, power requirements are of critical importance. One type of memory system often used in microprocessor applications is a static random access memory (SRAM) system.
SRAM systems comprise a memory cell array composed of SRAM memory cells. A wordline is associated with each row of SRAM memory cells, and a pair of bitlines are associated with each column of SRAM memory cells. Each SRAM memory cell includes a pair of complementary ports, with each port coupled to one of two bitlines dedicated to that column of SRAM memory cells.
When writing, or storing data, in a SRAM memory cell, the appropriate wordline is activated, thereby activating the entire row of memory cells in the SRAM memory cell array. A differential current is applied to the appropriate complementary bitlines that connect to each respective port of the SRAM memory cell. The SRAM memory cell is then latched to a specific logic state with a logic high indicated on one port and a logic low indicated on the other port. When reading from a SRAM system, the appropriate wordline is activated and the logic states on the bitlines associated with the memory cell are differentially sensed using a sense amplifier. The sense amplifier outputs an amplified data output signal that corresponds to the logic state written to the memory cell.
Activating the SRAM memory cells to retrieve the stored data requires time and uses power. Time and power are each valuable commodities in a memory system and must be minimized.